The present invention relates to a method for restoration of the drive torque during a change of gear, and in particular a change of gear carried out by a power-assisted control manual gearbox, to which the following description will refer specifically, without detracting from generality.
Power-assisted control manual gearboxes are becoming increasingly common, which are structurally altogether similar to a manual gearbox of the conventional type, with the exception of the fact that pedals and control levers which can be actuated by the user are replaced by corresponding electric or hydraulic power-assisted controls. When using a power-assisted control manual gearbox, the user simply needs to transmit to a control system the order to change to a higher gear or a lower gear, and the control system automatically carries out the change of gear, by acting on the butterfly valve control and on the various power-assisted controls.
In normal driving conditions, a power-assisted control manual gearbox is required to guarantee a high level of comfort to the passengers of the vehicle during the phases of change of gear; recent studies have shown that in order to guarantee a high level of comfort for the passengers, the change of gear must take place within short times, and without giving rise to oscillations which can be perceived by the passengers themselves.
On completion of the operations of change of gear, the clutch must be reclosed, in order to render the drive shaft and the primary shaft of the gearbox integral with one another; in particular, after having established the new ratio in an ascending change (i.e. when the new ratio is xe2x80x9clengthierxe2x80x9d than the preceding one), the vehicle proceeds at a speed which is virtually identical to the speed before the action of changing gear, the engine rotates at a speed which is substantially the same as that obtained for the vehicle by means of the preceding ratio, and the primary shaft of the gearbox rotates at a speed which is the same at that obtained for the vehicle by means of the new ratio, and thus rotates more slowly than the drive shaft.
In this situation, in order to reduce the change time to a minimum, the clutch should be closed in the shortest time possible; however, this operative method is acceptable only at the limit of sporting driving, since it induces a series of oscillations in the speed of travel of the vehicle, which can clearly be perceived by the passengers, with a consequent deterioration in running comfort.
In order to close the clutch on completion of the operations of change of gear, it is known to actuate progressively and simultaneously both the power-assisted control of the clutch, and the power-assisted control of the butterfly valve, such as to increase simultaneously and progressively both the torque transmitted by the clutch and the torque generated by the engine. However, it has been found that this methodology is capable of avoiding stresses which can be perceived by the passengers only if it is carried out within relatively very lengthy times.
The object of the present invention is to provide a method for restoration of the drive torque during a change of gear, which avoids the drawbacks described hereinabove and is, in particular, of easy and economical implementation.
According to the present invention, a method is provided for restoration of the drive torque during a change of gear, as described in claim 1.